1. Field of the Invention
This invention relates generally to an improved "hybrid" exposure control system for a photographic camera apparatus and, more particularly, to an improved "hybrid" exposure control system for a photographic camera apparatus having a selected overexposure capability at relatively close camera-to-subject distances.
2. Description of the Prior Art
So-called "hybrid" exposure control systems are well known in the art and generally operate to control exposure in response to both firing a flash lamp at an appropriate aperture size calculated to generally correspond to the determined camera-to-subject distance in accordance with the inverse square law of light propagation and the subsequent detection and integration of reflected artificial illumination from the scene to provide a shutter blade closing command signal. This makes possible an increased degree of exposure correction since a slight error in the determination of camera-to-subject range resulting in a corresponding error in the aperture size at which the flash lamp is fired can be easily compensated by the detection and integration of the reflected artificial illumination to provide the shutter blade closing command signal. Such "hybrid" exposure control systems are disclosed in U.S. Pat. No. 3,464,332, entitled "Automatic Exposure Control System", by R. H. Davison et al., issued Sept. 2, 1979, in common assignment herewith, U.S. Pat. No. 3,975,744, entitled "Automatic Exposure Control System", by B. K. Johnson et al., issued Aug. 17, 1976, and U.S. Pat. No. 4,047,190, entitled "Hybrid Exposure Control System Employing Dual Maximum Blade Displacement", by B. K. Johnson et al., issued Sept. 6, 1977. Such "hybrid" exposure control systems as those disclosed above contemplate only the use of an ordinary flash lamp as the source of artificial illumination since the burn time of an ordinary flash lamp is sufficiently long as to allow the exposure to be terminated by the closing shutter blades.
Most recently, however, a "hybrid" exposure control system utilizing an electronic flash or strobe of the quench type for its source of artificial illumination has been proposed as disclosed in U.S. patent application Ser. No. 442,238, entitled "Hybrid Camera Arrangement", filed Nov. 16, 1982, in common assignment herewith. In this "hybrid" exposure control system, a quench strobe is fired at an appropriate aperture size corresponding to the determined camera-to-subject distance and the strobe is subsequently quenched as a function of reflected scene light detected in correspondence with the reflected scene light admitted to the film plane during the exposure interval.
Such "hybrid" exposure control systems, however, regardless of whether an ordinary flash lamp or a quench strobe is utilized operate to ignite the source of artificial illumination at a "hybrid" aperture value that is slightly larger than the so-called "follow-focus" aperture which as is well known in the art is the appropriate exposure aperture size based on the determined camera-to-subject distance, i.e., focus distance, as computed from the inverse law of light energy propagation. Thus, the "hybrid" aperture has a slight overexposure capability throughout its range of values which can be compensated by either closing the shutter blades in cameras where a flash lamp is fired or by quenching the strobe in cameras where a quench strobe is fired.
Difficulties may arise, however, in camera systems which utilize a sonic rangefinder to determine camera-to-subject distances particularly in cases where the minor subjects are located relatively close to the camera and the principal subject are located at some greater distance from the camera. In such situations minor subjects located slightly forward of the principal subject can be detected by the sonic rangefinder and therefor result in the source of artificial illumination being ignited prematurely and at a substantially smaller aperture than required for adequate exposure. The slight degree of overexposure capability provided by the "hybrid" aperture will not be sufficient to overcome an underexposure of the film. Conversely, in situations where the minor subjects are located at substantially greater distances from the camera, the detection of minor subjects located slightly forward of the major subject will generally not result in the source of artificial illumination being ignited at an aperture value significantly smaller than the aperture required for adequate exposure, and thus the slight degree of overexposure capability provided by the "hybrid" aperture is unnecessary and may even result in an overexposure of the film.
Therefore, it is a primary object of this invention to provide an improved "hybrid" exposure control system wherein the "hybrid" aperture value at which a source of artificial illumination is ignited provides for a higher degree of overexposure capability for relatively short camera-to-subject distances than for longer camera-to-subject distances.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.